1. Field of the Invention
The present invention relates to an ultrasonic endoscope to be used for body cavity examination of upper digestive organs, bronchial tube, and so on, and the present invention further relates to an ultrasonic endoscopic apparatus including the ultrasonic endoscope.
2. Description of a Related Art
In medical fields, various imaging technologies have been developed in order to observe the interior of an object to be inspected and make diagnoses. Among them, especially, ultrasonic imaging for acquiring interior information of the object by transmitting and receiving ultrasonic waves enables image observation in real time and provides no exposure to radiation unlike other medical image technologies such as X-ray photography or RI (radio isotope) scintillation camera. Accordingly, ultrasonic imaging is utilized as an imaging technology at a high level of safety in a wide range of departments including not only the fetal diagnosis in the obstetrics, but also gynecology, circulatory system, digestive system, etc.
The ultrasonic imaging is an image generation technology utilizing the nature of ultrasonic waves that the ultrasonic waves are reflected at a boundary between regions with different acoustic impedances (e.g., a boundary between structures). Typically, an ultrasonic diagnostic apparatus is provided with a body surface ultrasonic probe to be used in contact with the object or intracavity ultrasonic probe to be used by being inserted into a body cavity of the object. Further, in recent years, an ultrasonic endoscope in combination of an endoscope for optically observing the interior of the object and an ultrasonic probe for intracavity has been used.
Ultrasonic beams are transmitted toward the object such as a human body and ultrasonic echoes generated in the object are received by using the ultrasonic endoscope, and thereby, ultrasonic image information is acquired. On the basis of the ultrasonic image information, ultrasonic images of structures (e.g., internal organs, diseased tissues, or the like) existing within the object are displayed on a display unit of an ultrasonic endoscopic apparatus main body connected to the ultrasonic endoscope.
As an ultrasonic transducer for transmitting and receiving ultrasonic waves, a vibrator (piezoelectric vibrator) having electrodes formed on both sides of a material that expresses a piezoelectric property (a piezoelectric material) is generally used. As the piezoelectric material, piezoelectric ceramics represented by PZT (Pb (lead) zirconate titanate), a polymeric piezoelectric material represented by PVDF (polyvinylidene difluoride), or the like is used.
When a voltage is applied to the electrodes of the vibrator, the piezoelectric material expands and contracts due to the piezoelectric effect and generates ultrasonic waves. Accordingly, plural vibrators are one-dimensionally or two-dimensionally arranged and the vibrators are sequentially driven, and thereby, an ultrasonic beam to be transmitted in a desired direction can be formed. Further, the vibrators expand and contract by receiving propagating ultrasonic waves and generate electric signals. These electric signals are used as reception signals of the ultrasonic waves.
When ultrasonic waves are transmitted, drive signals having great energy are supplied to the ultrasonic transducers. In this regard, not the entire energy of the drive signals is converted into acoustic energy but a significant proportion of the energy becomes heat, and there has been a problem that the temperature rises in use of the ultrasonic endoscope. However, the insertion part of the ultrasonic endoscope is used in direct contact with the living body such as a human body, and a request that the surface temperature of the insertion part of the ultrasonic endoscope is controlled to a predetermined temperature or less has been made for safety reasons of preventing low-temperature burn and so on.
As a related technology, Japanese Patent Application Publication JP-P2006-204552A discloses an ultrasonic probe in which the heat generated in a vibrator part and a circuit board is transferred to a shield case via a heat-conducting part, and the heat transferred to the shield case is absorbed by a heat absorbing part including a refrigerant feeder and a refrigerant pipe for cooling the vibrator part. However, a small-diameter endoscope such as a bronchial endoscope having an outer diameter of φ6.9 mm or less has no space for such a heat absorbing part including a refrigerant feeder and a refrigerant pipe.
Further, Japanese Registered Utility Model JP-Z-3061292 discloses that a heat transfer structure in contact with an integrated circuit within an ultrasonic transducer for extracting heat generated there to the outside is provided, and the extracted heat by the heat transfer structure is transferred to a conducting material that functions as a heat sink within a communication cable. However, the signal cable of the endoscope has a small sectional area, and, if the signal cable is used for heat dissipation, no sufficient heat dissipation effect is obtained due to the small sectional area.
In an ultrasonic endoscope to be used by being inserted into a body cavity of a patient, in order to reduce the physical stress on the patient to be examined, it is desired that the diameter of the insertion part is made smaller. Specifically, in body cavity examination of upper digestive organs, bronchial tube, and so on, a small-diameter endoscope having an outer diameter of φ6.9 mm is used, and downsizing of the ultrasonic endoscope becomes a challenge in view of reduction in physical stress on patients.
Further, in the ultrasonic endoscope, stacking the ultrasonic transducers to raise reception sensitivity is being considered for an improvement in diagnostic accuracy. However, as the transmission output of ultrasonic waves is increased by stacking the ultrasonic transducers, the amount of heat released from the ultrasonic transducers becomes larger. According to the structure of a conventional ultrasonic endoscope, if the transmission output of ultrasonic waves is increased by stacking the ultrasonic transducers, there is a problem that the temperature of the insertion part in contact with the inner wall of the body cavity rises due to the heat generation of the ultrasonic transducers. With downsizing of the ultrasonic endoscope, the temperature rise of the insertion part due to heat generation of the ultrasonic transducers has become an increasingly serious problem, and the problem is an issue to be solved.
Furthermore, when an imaging device (CCD or the like) and a light guide are attached to the insertion part of the ultrasonic endoscope, a problem of temperature rise in the insertion part due to heat generation from the imaging device and the light guide exit part arises, and the problem is an issue to be solved.